Aggregation assays are often prepared using spherical beads, whereupon the addition of the analyte causes the beads to aggregate. This change in particle size and behaviour is typically monitored using light scattering, absorption, or fluorescence to enable detection of an analyte. Multiplex detection may be achieved by either changing the diameter of the particles or one of their physical properties such as the colour it absorbs or emits light. However, there is a need for an improved method of detection of analytes in particular multiplex detection.